Question: Summing lists of lists of numbers

I have a list of lists. The number of lists I have is unknown (though always a positive integer) and the number of elements in each list is unknown (though, again, always a positive integer). Some examples: [[2],[3]]; [[4],[4],[5,1]]; [[3,4,1],[2],[2],[6,7]]; I'd like to form a list of all possible sums formed from one element of each list. The lists of sums from the examples above would be [6]; [13,9]; [13,14,11,14,15,12]; The order doesn't matter, and repeated elements don't matter. I can form these lists when I can control the number of lists in the large list and write an explicit nest of for loops. I figure there's got to be a more elegant and powerful way of producing these sums. Thanks in advance.
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